Trinitrotoluene manufacture



June l, 1946.

l C. F. PPAZON TRINITROTOLUENE MANUACTURE Filed July 4, 1942 HL TERN/TELY FR MNT lzdrls BY IN V EN TOR, v Ffa/45120111 WMMW.

Patented June 18, 1946 UNITED STATES PATENT OFFICE TRINITROTOLUENEMANUFACTURE Charles F. Papazoni, Allentown, Pa., assignor to TrojanPowder Company, a corporation of New York Application July 4, 1942,Serial No. 449,772

(c1. 26o-s45) v 2 Claims.

tion progressively from the mono to the tri-v stage, or conversely,decrease in concentration from the tri-stage to the mono-stage. Freshacids (oleum and mixed acid) are used onlyvin the tri-stage nitration.'Ihe tri and di-stage spent acids are fortified (butted up) with nitricacid to furnish the mixed acids used for the dinitration andmononitration, respectively. Thus, it is customary to use the spent acidfrom the trinitration, after fortification with fresh nitric acid, asthe mixed acid for the dinitration, and likewise, to fortify thedi-spent acid with nitric acid in making the mono-mixed acid. The spentacid from the mononitration is sent to the denitrator, for the recoveryof the nitric acid, and later to the sulfuric acid concentrator toprovide concentrated sulfuric acid. The mono.- spent, therefore, is theonly spent acid that leaves the nitrating system.

The spent acids from the di and trinitration are ordinarily withdrawnfrom the nitrators to mixing tanks in another building, there fortiiiedwith the required amount of nitric acid, and then dropped into a blowcase, a closed vessel adapted to withstand pressure. Compressed air isintroduced over the acid in this vessel and the acid forced bydisplacement under the pressure of the air from the blow case to areceiving (scale) tank in the proper nitrating building.

In the handling of this spent acid in the con- Ventional system, thereis some unavoidable corrosion of equipment and loss of nitric acid, notonly from the spent acid but also from the fortifying nitric acidintroduced into the mixing or fortifying tank and subsequently passed tthe blow case, scale tank, and back to the nitrator. Furthermore, thereare caused many delays in the operating system due to blowing of safetydiscs. plugging of standpipes, freezing of delivery lines, andoccasional explosions, for all of which the use of the blow case islargely responsible. These difficulties are especially pronounced withthe tri-spent acid after fortification. This trispent acid containsusually betweenv l5 and 18% of organic material, chiey TNT, and isfrequently responsible for blow case explosions in spent acidfortification and handling.

When the spent acidis thus fortified in the mixing'tank and held for ashort time at least in the blow case, the nitric acid added frequentlycauses further nitration to-a hazardous extent` of i'certain nitratableorganic material presentinthe spent acid. As the acid stands rfin theblow case, this reaction progressesV in the presence of the' compressedair and altogether too frequently there are explosions with destructionof buildings and equipment, resulting in delays in production aswell aspossible injury to workmen and surrounding property. 1

In the attempt to reduce blow case explosion hazards, the blow cases areordinarily provided with a safety sealvof sheet lead discs or the likewhich will rupture at certain set pressures, say 40 to 45 pounds to thesquare inch. These discs corrode, soften and weaken with age and use,

and frequently give wayunnecessarily. In replacing these discs some timeis required, during which delay there is often freezing or solidicationof organic matter in the standpipe (exit line) of the blow case or inthe delivery lines to the nitrating buildings so that these lines mustalso be opened up and freed of plugging material before acid can bedelivered from the blow case and dperations resumed. During Y coldweather, the delivery linev from the blow case to the nitrator buildingsvoften freeze when there has been no trouble in the blow case. Thereforethe elimination of the fortier building and the separate handling of thespent acids thru pipe lines, as in my invention, results in considerablesaving of time previously lost thru these difficulties.

The present invention vprovides a method of overcoming thesedi'iculties.

Briey stated, the present invention comprises leaving the spent acidfrom the trinitration stage in the nitrator, fortifying this spent acidin the nitrator itself, and to the resulting di-mixed acid addingmononitrotoluol (the reverse of the present practice). The inventioncomprises also settling and separation of the di-spent acid andtransferring it without the application of any .pressure upon it, to themono-nitrator where it is fortified to mono-mixed acid and used for themononitration. According to the invention,

pressure of approximately atmospheric is main- -tained upon the spentacids to bereusedrafter fortification, the said pressure beingmaintainedk at all times both before and after the fortifica- 'Y tion.For best results in reducing the manu- 3 facturing hazards, thetrl-spent acid is maintained at all times under observation and controland the temperature not allowed to rise substantially above 230 F.

According to this method, there is complete elimination of (l) the blowcase and the entire fortification building including its mixer tank andthe exposed acid lines from the blow case to the nitrator buildings, (2)application of either pump or air pressure to the di and tri-spentacids, and (3) transfer of any tri-spent in any manner.

Using this method, it is possible to increase the production of astandard TNT line by approximately iifty percent, due to shortening ofthe time required for butting up of spent acid, elimination oftransferring of same, shortening of the overall nitration time, andavoidance of the difficulties and delays involved in the use of the blowcase.

It will be understood that the nitrators, the compositions of all acidmixtures used in the several nitration stages, the spent acidcompositions, temperatures of nitrations, and all details not otherwisestated are those that are conventional in making DNT and TNT.

According to my method, the fortification of the spent acids for themono and dinitration is conducted under the same type of control as usedconventionally in making nitrations. In other words, at the time thefortifying nitric acid is added to the tri-spent or the di-spent acids,variations in temperature are recorded, the mixture is thoroughly andcontinuously agitated, the operations are observed through windowsproperly lighted, and the mixture cooled by cooling coils that areconventional in TNT nitrators to avoid any overheating. Thus, there isthe same careful control of conditions in butting up as previously usedheretofore only in the nitration step and is not possible in the blowcases. Since there is no pressure upon any of the spent and mixed acidsat any time in the operation, there is no possibility of confinementsuch as exists in blow cases which not only increases the possibility ofexplosion but also the extent of the resulting damage.

Attaining the advantages of this invention is facilitated by placing thedi and trinitrators at an elevation above the mononitrator, so that thespent acid from the dinitration step iiows downwardly through aconnecting line to the mononitrators. After a dinitration has beeneffected in a given nitration vessel, agitation is discontinued and theresulting di-spent acid is settled, withdrawn from the bottom of thenitrator, and dropped to the mononitrator where it is fortified to monomixed acid. To the dinitrotoluene left in the nitrator, oleum is addedand then tri-mixed acid in the usual way.

After the trinitration is thus effected, agitation is discontinued, andthe charge allowed to separate, then the TNT (top layer in the nitrator)is withdrawn, .by decantation thru outlets in the side of the nitratorand the spent acid is allowed to remain in the nitrator. This spent isfortified with nitric acid in situ for a dinitration. In other words,the di and trinitrators are used alternately for the di and trinitrationsteps. Ordinarily two of the di and tri-nitrators are required for onemononitrator for a plant of balanced capacity.

With my improved method as much as 30 to 60 minutes is saved on eachcycle of toluene nitrated to TNT with the consequent larger increase ofcapacity in standard TNT line.

'I'he method is illustrated diagrammatically iny the attached now sheetwhich forms a part of this speciiication and will be described for thepurpose of illustration in greater detail in connection with thedrawing.

Nitric acid is added in the mononitrator to butt up the there presentdi-spent acid separated from a previous nitration of the toluene to thedi-stage. During the addition of nitric acid, the di-spent acid isstirred continuously and the charge is cooled (as much as necessary) by@001mg coils that are usual in toluene nitrators to avoid overheatingdue to nitration of nitratable material in the spent acid. After thefortification is complete, toluene is added to the mono-mixed acid andstirring continued at the usual temperature for making mononitrotoluene.

After the nitration to mononitroluene is commercially complete, thestirring is discontinued, the charge settled and separated, and spentacid and mononitrotoluol drawn off and sent to respective houses forfurther treatment; mono spent acid to the recovery and mononitrotoluolto ditri houses for further nitration.

The mononitrotoluene so made is pumped to the di-nitrator. Here themononitrotoluene is stirred into a mixture of tri-spent acid which hasbeen fortified in situ with the required proportion of nitric acid tomake a di-inixed acid. After the nitration to the di-stage is complete,the di-spent is passed downwardly, under only atmospheric pressure uponits upper surface, into the mononitrator for fortification there andreuse in the mononitration stage as described.

After the cli-spent has been withdrawn from the dinitrator, there isadded to the dinitrotoluene there contained a fresh mixture of oleum andtrimixed acid in such proportion as to give the concentration ofsulfuric and nitric acids required for making TNT.

After this trinitration has been conducted under the usual conditions asto stirring, cooling, period of time, and temperature, then theagitation is discontinued, the charge settled, and the TNT withdrawn,from above the settled tri-- spent acid thru side openings in thenitrator to washing and subsequent purification and finishing operationswhich are conventional in TNT manufacture. The tri-spent is left in thenitrator and is there fortified by the addition of the calculatedquantity of nitric acid to make it suitable for (ii-mixed acid for whichpurpose the fortied material is then used with mononitrotoluene (MNT) tomake dinitrotoluene (DNT).

The di and trinitrators are interchangeable and are usually two innumber for each monontrator. One nitrator is used first in makingdinitrotoluene. Then the same nitrator is used in making a batch of thetrinitrotoluene, its next use being in making the dinitrotoluene. Inthis way, there is avoided any transference of the hazardous tri-spentacid and particularly transfer of this spent after fortification back tothe di-tri nitrator.

From the time the fortification of thedi and tri-spent acids isinitiated, the acids are stirred and under careful control, includingcooling, when necessary to maintain the temperature at a safe level,which for the more hazardous trispent acid is never substantially above230 F., until the fortification is complete, the resulting mixed acidshaving been used in nitration, and the acids having been again becomespent.

The di and trinitrators are located at an elevation above that of themononitrators, so that the di-spent acid flows by gravity through asuitable pipe line to the mononitrator.

It wil1 be understood also that it is intended to cover all changes andmodications of the example of the invention herein chosen for thepurpose of illustration which do not constitute departures from thespirit and scope of the invention.

What I claim is:

1. In making trinitrotoluene, the method which comprises running thespent acid, Without the application of pressure thereto, from thedinitration stage into the mono-nitrator, adding to the said spent acidthe required amount of nitric acid for fortification to mono-nitrationacid, adding toluene with stirring and nitratng the toluene tomononitrotoluene, discontinuing the stirring and removing the resultingmononitrotoluene from the mono-nitrator, fortifying tri-spent acid froma previous nitration in the vessel in which it was formed originallywith the required proportion of nitric acid to make di-nitration acid,introducing the mononitrotoluene gradually and with stirring into theresulting di-mixed acid to make dinitrotoluene, then discontinuing thestirring and transferring the di-spent acid, without the application ofpressure thereto, to the mono-nitrator for fortication there and forreuse in the mono-nitration stage as already described, agitating thedinitrotoluene in the nitrator where made with trinitrating acid toconvert the dinitrotoluene into trinitrotoluene, then discontinuing theagitation and withdrawing the trinitrotoluene from above the settledtri-spent acid, fortifying the tri-spent acid left in the nitrator bythe addition of the calculated quantity of nitric acid to make itsuitable for di-nitration acid, adding mononitrotoluene With stirring toth resulting di-nitration acid to make dinitrotoluene,-and continuingthe cycle of steps described.

2. In making trinitrotoluene by the method comprising nitration oftoluene in a plurality of stages with the formation of mono, di andtrispent acids and the use of fortified di and trispent acids insubsequent stages, the improvement which comprises carrying out thefollowing operations in the same nitrating vessel: nitration ofdinitrotoluene to trinitrotoluene by the addition of the tri-nitratingacid, separation of the resulting trinitrotoluene and tri-spent acid byremoving the trinitrotoluene layer leaving the tri-spent acid in thenitrator where formed, fortification of the tri-spent acid in situ toform di-nitrating acid; and addition of mononitrotoluene with stirringto the di-ntrating acid to form dinitrotoluene, discontinuing thestirring and separation of the dinitrotoluene from kthe di-spent acid byremoving the di-spent acid from the nitrator, and allowing thedinitrotoluene to remain in the nitrator ready for the tri-stagenitration as described above.

CHARLES F. PAPAZONI.A

